Fantasy fiction always revolves around magic or some other kind of supernatural force.

When discussing various types of fiction, it’s common for people to lump sci-fi and fantasy together, as if they were virtually the same genre.

To be fair, on a general level, this comparison certainly holds true. For example, both sci-fi and fantasy stories involve imaginary worlds, strange creatures and forces beyond those which we experience in the here and now. For this reason, the two genres also tend to appeal to the same sorts of readers, those who yearn for an escape from the everyday. But beyond these broad similarities, sci-fi and fantasy bear some key distinctions that most people tend to overlook or ignore.

You may think the need to distinguish between sci-fi and fantasy a minor point, yet another example of the perpetual hair-splitting that typifies the world of geekdom. But when it comes to writing in either of these genres, such distinctions are all-important.

If you’ve struggled to differentiate between the two genres, I’d like to offer two general rules to guide your thinking in this area.

1. Science fiction always revolves around the introduction of a disruptive technology.

Whether it’s time travel (Looper), artificial intelligence (2001: A Space Odyssey), the ability to predict crimes before they happen (Minority Report), artificial humans (Do Androids Dream of Electric Sheep?), terra-forming (Dune) or cloning (Brave New World), each sci-fi story revolves around a disruptive technology that completely reorders the world in its image.

Typically, when the technology is first introduced, it is viewed as good or at the worst, benign. But then something goes wrong, and the very people who created the technology or who benefited from it are now threatened by it, with the fate of the entire world potentially hanging in the balance. A struggle ensues to regain control over the technology, to destroy it or to prevent it from falling into evil hands. In the end, order is usually restored, but at a tremendous price and with lingering doubts about whether or not human “progress” is really all it’s cracked up to be.

This story pattern is similar whether the threat unleashed takes the form of a device or some sort of monster (Godzilla, Frankenstein) or alien (The Thing, Alien). In the latter case, it’s the monster rather than a device that must be defeated or destroyed. But in the end, the technology that gave rise to it often targeted for destruction as well. (Think of the mob descending upon Dr. Frankenstein’s lab.)

Science fiction stories may bend the laws of physics, but true or “hard” science fiction stories will never break them. Even if a sci-fi story appears to break one or more laws of physics, a plausible explanation will usually be offered to justify the apparent discrepancy. In this regard, although a story like Star Wars is often classified as science fiction, it is really more of a fantasy. The films certainly employ all sorts of technology, but the only truly disruptive power in the Star Wars universe is the Force, which is essentially a form of magic.

On a metaphorical level, sci-fi stories tend to reflect our ambivalence toward our own technological progress. Whether we’re talking nuclear weapons, surveillance technology, genetic modification of food, cloning or other forms of biotechnology, science fiction is a great way to explore the pros and cons of human curiosity and technological ability. While such stories tend to be pessimistic in tone, rather than an absolute rejection of technology, they are more often offered as cautionary tales.